I think you have given a clue as to the problem Riley

I presume you had the tank off for the plug change etc. ?
Often a trapped fuel/breather pipe can present these symptoms

Particularly with "vacuum" type fuel taps

Is yours a diaphram tap ?
(Yams usually are

)
Could be a classic case of fuel starvation m8

Don't abandon all hope yet

It's quite likely to be something minor